The invention relates to locating a curved object in a three-dimensional array of data, and especially, but not exclusively, to locating an unevenly curved structure in a tomographic imaging dataset. The invention has particular application to locating the maxilla, the mandible, or both in a dataset of part of the head of a human or other mammal.
In certain forms of dental medicine and surgery, a “panoramic” image of the jaw is used to examine the jaw, for example, for monitoring of dental health and condition, diagnosis, and planning of prosthetic and other surgical procedures. The panoramic image of the jaw, like a panoramic photograph, depicts the jaw as if it were imaged onto an imaginary approximately cylindrical sheet with the axis of the sheet upright, and the sheet were then unrolled into a flat form. However, the human jaw is not a perfect circular arc, so the “cylindrical” shape of the imaginary sheet is not exactly circular.
A set of three-dimensional data relating to a property of an object that varies over space within the object may be obtained in various ways. For example, an x-ray image of a target may be obtained by placing the target between a source of x-rays and a detector of the x-rays. In a computed tomography (CT) system, a series of x-ray images of a target are taken with the direction from the source to the detector differently oriented relative to the target. From these images, a three-dimensional representation of the density of x-ray absorbing material in the target may be reconstructed. Other methods of generating a three-dimensional dataset are known, including magnetic resonance imaging, or may be developed hereafter.
From the three-dimensional data, a desired section or “slice” may be generated, including a curved slice. For example, a slice curving along the jaw, corresponding to a panoramic view of the jaw may be generated, provided that the position of the jaw within the three-dimensional dataset is known. It has previously been proposed to display on a visual display unit (VDU) a horizontal section through the mandible or maxilla, and for a human user to identify, for example by controlling a cursor on the VDU or by using a stylus on a touch-sensitive VDU, enough points on the mandible or maxilla for the curve of the jaw to be interpolated. However, many dentists and oral surgeons are not skilled computer operators.
There is therefore a hitherto unfulfilled need for a system by which the arc of the jaw can be accurately identified in a tomographic dataset without relying on the skill of a human operator, so that panoramic and similar images can be reliably automatically generated.